We've seen some homebrew solutions for adding a battery meter on the today screen before, but now with Mango, devs have a lot more options to choose from, including local updates.
Over at XDA, member singularity0821 has come up with a new battery meter called Mango Battery Status and it just hit version 3.3. What makes this app much nicer than the previous noble attempt is it has a double-sided Live Tile, showing that battery percentage remaining on one side and the status (charging, discharging) on the other. Tapping it of course launches the mini-app showing your current battery level, acting as a tile refresh.
You can also record your battery history over time to see how well the battery holds up--great for doing some testing of hardware. The app only requires your device be unlocked and not interop-unlocked, meaning just about everyone can do this now with the ChevronWP7 Labs available. We approve!
Source: XDA; Thanks, Ryan, for the heads up!